Linear actuators, which impart linear motion to a movable member such as a table and cause the movable member to stop at a predetermined position, are frequently used for various kinds of tables of machine tools, the moving portion of industrial robots, various kinds of conveying devices, and the like. Conventionally, with respect to the linear actuators of this type, known examples of driving means for imparting a propulsion force or brake force to the movable member include one which converts the rotation of a motor into linear motion by using a ball screw and one which converts the rotation of a motor into linear motion by using an endless timing belt wound around a pair of pulleys. Recent years have seen the appearance of various types of actuators employing a linear motor as drive means, that is, linear, motor actuators.
As the most common type of linear motor actuators, there is known one in which the movable member is supported on a stationary portion such as a bed or a column by using a pair of linear guides so that the movable member is free to reciprocate, and in which a stator and a mover that constitute a linear motor are respectively mounted to the stationary portion and the movable member so as to be opposed to each other (JP 10-290560A and the like). Specifically, a track rail of each linear guide is arranged in the stationary portion and the stator of the linear motor is mounted in parallel to the track rail, and a slider of the linear guide and the mover of the linear motor are mounted to the movable member; by incorporating the slider on the movable member side into the track rail, the movable member is supported on the stationary member so as to freely reciprocate, and the stator on the stationary portion side and the mover on the movable member side are opposed to each other.
With linear motor actuators, the parallelism between the track rail of the linear guide and the stator of the linear motor is important in securing the accuracy of the movement of the movable member, and it is also important, for the purpose of attaining a sufficient propulsion force, that the stator and mover of the linear motor be opposed to each other through a predetermined air gap. However, in the case of the linear motor actuators whose linear guide and linear motor are completely separated from each other as described above, it is extremely difficult and troublesome to perform the assembly while taking the above requirements into consideration.
Typical examples of linear motors include so-called synchronous motors composed of a field magnet employing a permanent magnet and of an armature around which a coil is wound. As the synchronous motors, there exist those of a core-attached type having a core formed of a magnetic member and those of a core-less type with no such core attached. Although the core-attached type ones prove effective from the viewpoint of obtaining a large propulsion force, due to the existence of the core, a magnetic attraction force equivalent to several times of the propulsion force is exerted between the armature and the field magnet even when no electric current is passed through the armature. For this reason, the above-mentioned assembly operation becomes even more difficult in the case where such a core-attached type linear motor is adopted.
On the other hand, known examples of linear motor actuators in which the linear guide and the linear motor are integrated together include those disclosed in JP 05-227729 A and JP 2001-25229 A. In the linear motor actuator of the former type disclosed in JP 05-227729 A, a recessed groove is formed in the track rail along the longitudinal direction thereof, with the armature being received within the recessed groove, and the slider is formed in a saddle-like configuration straddling the track rail. In the slider, the field magnet is fixed at a position opposed to the armature on the track rail side; when electric current is passed through the armature, a propulsion force is exerted on the slider incorporating the field magnet due to the Fleming's left-hand rule, so the slider moves along the track rail. That is, this linear motor actuator is a movable magnet type linear motor actuator having the field magnet as a mover.
However, with the movable magnet type linear motor actuator, the armature must be provided over the entire length of the track rail, and in order to set the resolution of the actuator with high accuracy, the armature coil must be finely segmented. Accordingly, when a large stroke length is set for the slider, this not only makes the preparation of the armature coil rather troublesome but also causes an increase in cost.
In contrast, the linear motor actuator of the latter type disclosed in JP 2001-25229 A is a so-called movable coil type one in which the armature moves together with the slider. That is, the field magnet is directly fixed to the track rail of the linear guide, and the armature is mounted in the slider; when electric current is passed through the armature to excite the armature coil, the slider incorporating the armature moves along the track rail.
However, with the above linear motor actuator, although the armature and the field magnet are fixed to the slider and track rail of the linear guide, respectively, they are externally fixed without being incorporated in the track rail and the slider, so the size of the actuator itself disadvantageously increases. Further, there is a risk that the field magnet or the armature may come into contact with peripheral equipment during the transport operation or the mounting operation thereof to the stationary portion such as a bed, resulting in damage.